1. Field of the Invention
The present invention relates to an apparatus for processing audio signals. Particularly, this invention relates to an apparatus that processes high pitch audio signals for easier listening.
2. Description of the Related Art
There are demands for rapid reproduction of audio signals from a recording medium, such as a magnetic tape by a reproducing apparatus, such as a video tape recorder (VTR) under the condition that the reproducing tape speed is higher than the recording tape speed.
In such reproduction, a relative speed between a recording/reproducing head and a recording tape becomes higher than that in recording. This results in higher reproduced audio signal frequency than recording audio signal frequency with listening difficulty.
Some apparatuses have been introduced that resolve such a difficulty by rapidly sampling audio signals reproduced from a magnetic tape and writing them into a semiconductor memory and quickly reading them to obtain a lower reproduced signal frequency than a recording signal frequency for easier listening.
Such apparatuses are disclosed in Japanese Patent No. 7(1995)-120158 and Japanese Patent Laid-Open No. 3(1991)-205656. In the disclosed apparatuses, audio signals of a predetermined quantity (one block) are rapidly sampled, written in a semiconductor memory and then quickly read therefrom.
The apparatus disclosed in the former Japanese Patent is to resolve the following problem: One block data quantity is usually a storage capacity of a semiconductor memory. Audio signals are written in the memory as a continuous signal without intermission from the minimum to the maximum memory addresses. This results in listening difficulty due to short one-block length and short time for continues listening without memory of huge storage capacity.
Further, the apparatus disclosed in the latter Japanese Laid-Open Patent is to inhibit memory writing at silent portions by removing those portions from audio signals for easier listening of continuous sound. This is accomplished by halting advances in reading address when a writing address and a reading address become identical to each other at silent portions.
However, in these apparatuses, new memory writing is sometimes never carried out due to halting of the advance in reading address under identicalness of the writing and reading addresses. This will happen even not at the silent portions in the latter apparatus. And, this results in repeating of reading data that has been already read from the memory, thus causing listening difficulty. Such difficulty will be caused when address writing and reading clock timings are not matched each other or the number "M" of M-speed reproduction is not an integral number.